Ferroelectric ceramic material

ABSTRACT

The present invention relates to a ferroelectric ceramic material which is a Perovskite solid solution comprising a solid solution represented by the formula: 
     
         Pb.sub.1-a M.sub.a (Mg.sub.1/3 p0 Nb.sub.2/3).sub.x Ti.sub.y Zr.sub.z 
    
      O 3   
     containing in the solution at least one oxide selected from the group A noted below and at least one oxide selected from the group B noted below. 
     Group A : La 2  O 3  and Nd 2  O 3  ; 
     Group B : ZnO, SnO 2  and Ta 2  O 5 . 
     The proposed ferroelectric ceramic material has a large piezoelectric strain constant d. The present invention is further directed to ferroelectric ceramic which is a Perovskite solid solution comprising a solid solution represented by the formula: 
     
         Pb.sub.1 -aM.sub.a (Mg.sub.1/3  Nb.sub.2/3).sub.x Ti.sub.y Zr.sub.z O.sub.3 
    
     wherein M is Ba or Sr, x+y+z is 1, a is from 0 to 0.10, x is from 0.05 to 0.70, y is from 0.25 to 0.50 and z is from 0.05 to 0.70, containing in the solution at least one oxide selected from the group A noted below and at least one oxide selected from the group B noted below, the solid solution further containing in the solid solution MnO 2 . 
     Group A : La 2  O 3  and Nd 2  O 3  ; 
     Group B : ZnO and SnO 2 .

FIELD OF THE INVENTION

The present invention relates to a ferroelectric ceramic material of Pb (Mg_(1/3) Nb_(2/3)) O₃ --PbTiO₃ --PbZrO₃ series. More particularly, the present invention relates to a ferroelectric ceramic material of Pb (Mg_(1/3) Nb_(2/3)) O₃ --PbTiO₃ --PbZrO₃ series having a large piezoelectric strain constant d and an excellent mechanical quality factor Q_(m).

BACKGROUND OF THE INVENTION

Piezoelectric materials comprising ferroelectric ceramic materials have heretofore been used in piezoelectric filters, piezoelectric transducers, ultrasonic oscillators and piezoelectric buzzers. The most typical ferroelectric ceramic materials that have been used in such applications are solid solutions of PbTiO₃ --PbZrO₃ series. Solid solutions of Pb (Mg_(1/3) Nb_(2/3)) O₃ --PbTiO₃ PbZrO₃ series (Japanese Patent Publication No. 42-9716) and those further containing BaTiO₃, SrTiO₃ and/or CaTiO₃ are also known as having improved piezoelectric characteristics.

On the other hand, the use of piezoelectric ceramic materials as an actuator has also been recently studied. In this case, it is necessary to transform electric energy to mechanical energy by the displacement of the piezoelectric ceramic material itself by the so transformed mechanical energy. Accordingly, piezoelectric ceramic materials having a large piezoelectric strain constant d are desired.

The piezoelectric strain constant d, is related to an electromechanical coupling factor k and a relative dielectric constant ε, of a piezoelectric ceramic material, as follows: ##EQU1## and therefore, in order that the material has a large piezoelectric strain constant d, it must have a large electromechanical coupling factor k and/or a large relative dielectric constant ε.

Further, in applications of piezoelectric ceramic materials such as a driving part of an actuator, for example, an ultrasonic motor, where mechanical resonance of the material is utilized, it is desired that both the piezoelectric strain constant d and the mechanical quality factor Q_(m) are large. When a piezoelectric ceramic material is used in an ultrasonic motor, if the mechanical quality factor Q_(m) of the material is small, heat is generated due to high frequency driving involved, frequently leading to undesirable reduction in spontaneous polarization of the material and changes in the piezoelectric strain constant of the material with time. Accordingly, it is essential that the mechanical quality factor Q_(m) of a piezoelectric ceramic material be large, when the material is to be used in ultrasonic motors.

While the mechanical quality factor Q_(m) of solid solutions of PbTiO₃ --PbZrO₃ series or of Pb (Mg_(1/3) Nb_(2/3)) O₃ --PbTiO₃ --PbZrO₃ series can be improved by incorporation of MnO₂ thereinto, there has been a problem in that the piezoelectric strain constant d of the material is drastically decreased as the amount of the MnO₂ added increases. Accordingly, base solid solutions prior to the addition of MnO₂ thereto should preferably have a sufficiently large piezoelectric strain constant d.

While various attempts have heretofore been made to add various oxides to solid solutions of Pb (Mg_(1/3) Nb_(2/3)) O₃ --PbTiO₃ --PbZrO₃ series optionally containing BaTiO₃, SrTiO₃ and/or CaTiO₃ for the purpose of increasing the electromechanical coupling factor k and/or relative dielectric constant ε, of the solid solutions, thereby increasing the piezoelectric strain constant d of the materials, the attainable level of the piezoelectric strain constant d has not necessarily been satisfactory.

For example, when a solid solution of Pb (Mg_(1/3) Nb_(2/3)) O₃ --PbTiO₃ --PbZrO₃ series optionally containing BaTiO₃, SrTiO₃ and/or CaTiO₃ is incorporated with NiO, the piezoelectric strain constant d of the material is increased as the amount of NiO added is increased. However, when the amount of NiO added exceeds a certain limit, the piezoelectric strain constant d of the material is rather decreased. This is believed because whereas Ni ions preferentially enter the B sites of the Perovskite crystals represented by ABO₃, if the amount of NiO admixed with the Perovskite crystals exceeds a certain limit, ions in the A sites of the crystals becomes short and, as a consequence a part of the NiO admixed can no longer enter the B sites of the Perovskite crystals.

It has now been found that if Perovskite crystals are incorporated with metal ions which enter the A sites of the crystals in addition to metal ions which enter the B sites of the crystal, such as Ni ions, ferroelectric ceramic materials having a larger piezoelectric strain constant d are obtained when compared to the case wherein the Perovskite crystals are incorporated with metal ions which enter only the B sites. It has also been found that if the so obtained ferroelectric ceramic solid solutions having a large piezoelectric strain constant d are further incorporated with MnO₂, ferroelectric ceramic materials having large piezoelectric strain constant d and mechanical quality factor Q_(m) are obtained.

SUMMARY OF THE INVENTION

The invention is based on the above-mentioned findings and accordingly an object of the invention is to provide ferroelectric ceramic materials having a large piezoelectric strain constant d and an excellent mechanical quality factor Q_(m), and as a consequence, which are excellent in piezoelectric characteristics and are suitable for use in an actuator.

A first ferroelectric ceramic material according to the invention is a Perovskite solid solution comprising a solid solution represented by the formula:

    Pb.sub.1-a M.sub.a (Mg.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y Zr.sub.z O.sub.3

wherein M is Ba or Sr, x+y+z is 1, a is from 0 to 0.10, x is from 0.05 to 0.70, y is from 0.25 to 0.50 and z is from 0.05 to 0.70, containing in said solution at least one oxide selected from the group A noted below and at least one oxide selected from the group B noted below.

Group A: La₂ O₃ and Nd₂ O₃ ;

Group B: ZnO, SnO₂ and Ta₂ O₅.

The first ferroelectric ceramic material according to the invention in which metal ions of oxides selected from the group A and metal ions of oxides selected from the group B are incorporated in the A and B sites of the ABO₃ type Perovskite crystals, respectively, has a greatly improved piezoelectric strain constant d when compared with known ferroelectric ceramic materials. Accordingly, the first ferroelectric ceramic material according to the invention exhibits excellent characteristics when used in applications such as an actuator.

The second ferroelectric ceramic material according to the invention is a Perovskite solid solution comprising a solid solution represented by the formula:

    Pb.sub.1-a M.sub.a (Mg.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y Zr.sub.z O.sub.3

wherein M is Ba or Sr, x+y+z is 1, a is from 0 to 0.10, x is from 0.05 to 0.70, y is from 0.25 to 0.50 and z is from 0.05 to 0.70, containing in said solution at least one oxide selected from the group A noted below and at least one oxide selected from the group B noted below, said solid solution further containing in said, solid solution MnO₂.

Group A: La₂ O₃ and Nd₂ O₃ ;

Group B: ZnO and SnO₂.

The second ferroelectric ceramic material according to the invention in which metal ions of oxides selected from the group A and metal ions of oxides selected from the group B are incorporated in the A and B sites of the Perovskite crystals, respectively, and in which MnO₂ is further incorporated, when compared with known ferroelectric ceramic materials, has an improved piezoelectric strain constant d, while retaining a comparable mechanical quality factor Q_(m). Accordingly, the second ferroelectric ceramic material according to the invention exhibits excellent characteristics when used in applications such as a driving part of an actuator, including an ultrasonic motor wherein mechanical resonance of the material is utilized.

DETAILED DESCRIPTION OF THE INVENTION

The ferroelectric ceramic materials according to the invention will now be described in detail.

The first ferroelectric ceramic material according to the invention is a Perovskite solid solution comprising a solid solution represented by the formula:

    Pb.sub.1-a M.sub.a (Mg.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y Zr.sub.z O.sub.3

wherein M is Ba or Sr, x+y+z is 1,

a is from 0 to 0.10, preferably from 0.01 to 0.07,

x is from 0.05 to 0.70, preferably from 0.10 to 0.60,

y is from 0.25 to 0.50, preferably from 0.30 to 0.45, and

z is from 0.05 to 0.70, preferably from 0.10 to 0.60,

containing in said solution at least one oxide selected from the group A noted below and at least one oxide selected from the group B noted below.

Group A: La₂ O₃ and Nd₂ O₃ ;

Group B: ZnO, SnO₂ and Ta₂ O₅.

When the Perovskite crystals constituting the first ferroelectric ceramic material according to the invention are represented by ABO₃, a metal of at least one oxide selected from the group A is present in A sites of the crystals in the form of metal ions as noted below, and a metal of at least one oxide selected from the group B is present in B sites of the crystals in the form of metal ions as noted below.

Group A: (La³⁺ or Nd³⁺)

Group B: (Zn²⁺, Sn⁴⁺ or Ta⁵⁺).

In the solid solution represented by the formula:

    Pb.sub.1-a M.sub.a (Mg.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y Zr.sub.z O.sub.3

wherein M is Ba or Sr, metal ions of the group A are present preferably in an amount of from 0.5 to 5.0 atom equivalents based on 100 atom equivalents of the sum of Pb and M present in the solid solution. With such an amount of metal ions of the group A, a particularly improved piezoelectric strain constant d can be achieved. The metal ions of the group B are present in the Perovskite solid solution preferably in such an amount so that the relation:

    0.5≦N≦5.0

is met, in which N is a defined by the equation: ##EQU2## wherein n_(Ai) and n_(Bj) are valencies of metal ions of the oxides of groups A and B which are present in the solid solution, respectively, and x_(Ai) and x_(Bj) are atom equivalents of metal ions of the oxides of groups A and B which are present in the solid solution, respectively. With such an amount of metal ions of the group B, a particularly improved piezoelectric strain constant d can be achieved.

The second ferroelectric ceramic material according to the invention is a Perovskite solid solution comprising a solid solution represented by the formula:

    Pb.sub.1-a M.sub.a (Mg.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y Zr.sub.z O.sub.3

wherein M is Ba or Sr, x+y+z is 1,

a is from 0 to 0.10, preferably from 0.01 to 0.07,

x is from 0.05 to 0.70, preferably from 0.10 to 0.60,

y is from 0.25 to 0.50, preferably from 0.30 to 0.45, and

z is from 0.05 to 0.70, preferably from 0.10 to 0.60,

containing in said solution at least one oxide selected from the group A noted below and at least one oxide selected from the group B noted below, said solid solution further containing in said solution MnO₂.

Group A: La₂ O₃ and Nd₂ O_(3;)

Group B: ZnO and SnO₂.

When the Perovskite crystals constituting the second ferroelectric ceramic material according to the invention are represented by ABO₃, a metal of at least one oxide selected from the group A is present in the A sites of the crystals in the form of metal ions as noted below, and a metal of at least one oxide selected from the group B is present in the B sites of the crystals in the form of metal ions as noted below.

Group A: (La³⁺ or Nd³⁺); and

Group B: (Zn²⁺ or Sn⁴⁺).

In the solid solution represented by the formula:

    Pb.sub.1-a M.sub.a (Mg.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y Zr.sub.z O.sub.3

wherein M is Ba or Sr, metal ions of the group A are present preferably in an amount of from 0.5 to 5.0 atom equivalents based on 100 atom equivalents of the sum of Pb and M present in the solid solution. With such an amount of metal ions of the group A, a particularly improved piezoelectric strain constant d can be achieved. The metal ions of the group B are present in the Perovskite solid solution in such an amount so that the relation:

    0.5≦N≦5.0

is met, in which N is a defined by the equation: ##EQU3## wherein n_(Ai) and n_(Bj) are valencies of metal ions of the oxides of groups A and B which are present in the solid solution, respectively, and x_(Ai) and x_(Bj) are atom equivalents of metal ions of the oxides of groups A and B which are present in the solid solution, respectively. With such an amount of metal ions of the group B, a particularly improved piezoelectric strain constant d can be achieved.

The amount of MnO₂ contained in the second ferroelectric ceramic material according to the invention is preferably from 0.1 to 2.0% by weight. With such an amount of MnO₂ contained in the ceramic material, an improved mechanical quality factor Q_(m) can be achieved, while retaining the piezoelectric strain constant d at a satisfactorily high level.

The ferroelectric ceramic materials according to the invention can be prepared by admixing particulate metal compounds such as oxides and salts in such proportions which provide a desired composition when calcined, and calcining the admixture. Processes for preparing the starting particulate metal compounds are not particularly limited. They may be prepared by various known processes, including liquid phase processes such as precipitation, coprecipitation, alkoxide and sol-gel processes, and solid phase processes such as those based on decomposition of oxalates and blending of oxides. The admixture of particulate metal compounds in appropriate proportions may be pre-calcined at a temperature of from 800° to 1000° C., pulverized in a ball mill, dried, pressed to a sheet under a pressure of from 500 to 1500 kg/cm², and finally calcined at a temperature of from 1000° to 1300° C., whereupon a desired ferroelectric ceramic material may be obtained.

EXAMPLES

While the invention will now be described by the following examples, it should be appreciated that the invention is in no way restricted to the examples.

The radial electromechanical coupling factor Kp, relative dielectric constant ε and piezoelectric strain constant d₃₁ and mechanical quality factor Qm of ferroelectric ceramic materials were measured in accordance with Japan Electronic Material Manufactures Association Standard (EMAS).

EXAMPLES 1 TO 5, AND COMPARATIVE EXAMPLES 1

PbO, ZrO₂, TiO₂, MgCO₃, Nb₂ O₅, SrCO₃, La₂ O₃, ZnO and SnO₂ were weighed in proportions which provide each composition as indicated in Table 1, pulverized and admixed in a ball mill. The pulverized admixture was pre-calcined at a temperature of from 800° to 1000° C. for a period of from 1 to 2 hours, pulverized in a ball mill and dried. The mixture was then pressed to a disc having a diameter of 25 mm under a pressure of about 1000 kg/cm² and finally calcined at a temperature of 1050° to 1250° C. for a period of 1 to 2 hours.

The calcined disc so prepared was polished to a thickness of 0.5 mm, coated with silver paste on both surfaces and baked. It was then polarized by application of a DC electric field of 20 to 40 KV/cm in a silicone oil and thereafter aged for 12 hours. The specimen so prepared was tested for various electric properties.

The results are shown in Table 1. In Table 1, a, x, y and z represent coefficients appearing in the formula:

    Pb.sub.1-a Sr.sub.a (Mg.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y Zr.sub.z O.sub.3 [x+y+Z=1],

p, q and r represent atom equivalents of respective metal ions indicated in the same table based on 100 atom equivalents of the sum of Pb and Sr, and N is a value defined by the equation: ##EQU4## wherein n_(Ai) and n_(Bj) are valencies of metal ions of the groups A and B, respectively, and x_(Ai) and x_(Bj) are atom equivalents of metal ions of the groups A and B, respectively.

                                      TABLE 1                                      __________________________________________________________________________            Composition                        Electric Properties                                     Group A Metal Ion                                                                        Group B Metal Ion                                                                              Kp                                                                               d.sub.31                               a  x  y  z  p         q    r    N  ε                                                                         % × 10.sup.-12              __________________________________________________________________________                                                    m/V                             Example 1                                                                             0.05                                                                              0.375                                                                             0.375                                                                             0.250                                                                             La.sup.3+ 2.0                                                                            Zn.sup.2+ 2.0                                                                       Sn.sup.4+ 2.0                                                                       2.0                                                                               6360                                                                              63                                                                               353                             Example 2                                                                             0.05                                                                              0.375                                                                             0.375                                                                             0.250                                                                             La.sup.3+ 2.0                                                                            Zn.sup.2+ 2.0                                                                       --   0.67                                                                              5700                                                                              60                                                                               305                             Example 3                                                                             0.05                                                                              0.375                                                                             0.375                                                                             0.250                                                                             La.sup.3+ 1.0                                                                            Zn.sup.2+ 1.0                                                                       Sn.sup.4+ 1.0                                                                       2.0                                                                               5660                                                                              63                                                                               330                             Example 4                                                                             0.05                                                                              0.375                                                                             0.375                                                                             0.250                                                                             La.sup.3+ 1.0                                                                            Zn.sup.2+ 2.0                                                                       Sn.sup.4+ 2.0                                                                       4.0                                                                               4620                                                                              63                                                                               306                             Example 5                                                                             0.05                                                                              0.375                                                                             0.375                                                                             0.250                                                                             La.sup.3+ 0.5                                                                            Zn.sup.2+ 0.5                                                                       Sn.sup.4+ 0.5                                                                       2.0                                                                               4390                                                                              62                                                                               297                             Comp. Ex 1                                                                            0.05                                                                              0.375                                                                             0.375                                                                             0.250                                                                             --        --   --   -- 4100                                                                              61                                                                               267                             __________________________________________________________________________

It is revealed from Table 1 that when compared with the ferroelectric ceramic material [I] of Comparative Example 1 having a composition of the formula:

    Pb.sub.0.95 Sr.sub.0.05 (Mg.sub.1/3 Nb.sub.2/3).sub.0.375 Ti.sub.0.375 Zr.sub.0.250 O.sub.3,

the ferroelectric ceramic materials of Examples 1 to 5 according to the invention, which comprises the ferroelectric ceramic material [I] having incorporated with La³⁺ in the A sites and with Zn²⁺, or Zn²⁺ and Sn⁴⁺ in the B sites, do have a larger piezoelectric strain constant d₃₁.

EXAMPLES 6 TO 9

PbO, ZrO₂, TiO₂, MgCO₃, Nb₂ O₅, SrCO₃, at least one oxide selected from the group A consisting of La₂ O₃ and Nd₂ O₃, and at least one oxide selected from the group B consisting of ZnO, SnO₂ and Ta₂ O₅, were weighed in proportions which provide each composition as indicated in Table 2, pulverized and admixed in a ball mill. The pulverized admixture was processed as in Example 1 to prepare a ferroelectric ceramic material, which was tested for electric properties.

The results are shown in Table 2.

                                      TABLE 2                                      __________________________________________________________________________     Composition                               Electric Properties                                    Group A Metal Ion                                                                        Group B Metal Ion                                                                               Kp                                                                               d.sub.31                        a        x  y  z  p         q     r     N ε                                                                         % × 10.sup.-12              __________________________________________________________________________                                                    m/V                             Example 6                                                                            0.05                                                                              0.375                                                                             0.375                                                                             0.250                                                                             La.sup.3+ 2.0                                                                            Zn.sup.2+ 1.71                                                                       Ta.sup.5+ 1.71                                                                       2.0                                                                              6220                                                                              64                                                                               360                             Example 7                                                                            0.05                                                                              0.375                                                                             0.375                                                                             0.250                                                                             La.sup.3+ 1.0                                                                            Zn.sup.2+ 0.86                                                                       Ta.sup.5+ 0.86                                                                       2.0                                                                              5600                                                                              62                                                                               315                             Example 8                                                                            0.05                                                                              0.375                                                                             0.375                                                                             0.250                                                                             Nd.sup.3+ 2.0                                                                            Zn.sup.2+ 2.0                                                                        Sn.sup.4+ 2.0                                                                        2.0                                                                              6070                                                                              63                                                                               341                             Example 9                                                                            0.05                                                                              0.375                                                                             0.375                                                                             0.250                                                                             Nd.sup.3+ 2.0                                                                            Zn.sup.2+ 1.71                                                                       Ta.sup.5+ 1.71                                                                       2.0                                                                              5970                                                                              64                                                                               338                             __________________________________________________________________________

Table 2 also reveals that joint inclusion of metal ions of the groups A and B into the ferroelectric ceramic material [I] improves the piezoelectric strain constant d₃₁.

EXAMPLES 10 TO 12, AND COMPARATIVE EXAMPLES 2 TO 4

Each of the ferroelectric ceramic materials of the formula:

    Pb.sub.1-a Sr.sub.a (Mg.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y Zr.sub.z O.sub.3 [x+y+Z=1],

wherein the coefficients a, x, y and z are different from those of the ferroelectric ceramic material used in Examples 1 to 9, as indicated in Table 3, with (Examples 10 to 12) or without (Comparative Examples 2 to 4) La³⁺, Zn²⁺ and Sn⁴⁺ in amounts indicated in Table 3 incorporated therein, was prepared and tested for electric properties in the manner as described in Example 1.

The results are shown in Table 3.

EXAMPLE 13 AND COMPARATIVE EXAMPLE 5

Ferroelectric ceramic materials were prepared and tested in the same manner as described in Example 1 and Comparative Example 1, except that the SrCO₃ was replaced with the equimolar amount of BaCO₃.

The results are shown in Table 3.

                                      TABLE 3                                      __________________________________________________________________________            Composition                        Electric Properties                                     Group A Metal Ion                                                                        Group B Metal Ion                                                                              Kp                                                                               d.sub.31                               a  x  y  z  p         q    r    N  ε                                                                         % × 10.sup.-12              __________________________________________________________________________                                                    m/V                             Example 10                                                                            0.05                                                                              0.500                                                                             0.370                                                                             0.130                                                                             La.sup.3+ 2.0                                                                            Zn.sup.2+ 2.0                                                                       Sn.sup.4+ 2.0                                                                       2.0                                                                               6440                                                                              59                                                                               330                             Comp. Ex 2                                                                            0.05                                                                              0.500                                                                             0.370                                                                             0.130                                                                             --        --   --   -- 4690                                                                              56                                                                               262                             Example 11                                                                            0.05                                                                              0.130                                                                             0.430                                                                             0.440                                                                             La.sup.3+ 2.0                                                                            Zn.sup.2+ 2.0                                                                       Sn.sup.4+ 2.0                                                                       2.0                                                                               5780                                                                              61                                                                               325                             Comp. Ex 3                                                                            0.05                                                                              0.130                                                                             0.430                                                                             0.440                                                                             --        --   --   -- 3870                                                                              59                                                                               250                             Example 12                                                                            0.03                                                                              0.375                                                                             0.375                                                                             0.250                                                                             La.sup.3+ 3.0                                                                            Zn.sup.2+ 1.5                                                                       Sn.sup.4+ 3.0                                                                       1.67                                                                              5800                                                                              61                                                                               327                             Comp. Ex 4                                                                            0.03                                                                              0.375                                                                             0.375                                                                             0.250                                                                             --        --   --   -- 3480                                                                              59                                                                               240                             Example 13                                                                            0.05                                                                              0.375                                                                             0.375                                                                             0.250                                                                             La.sup.3+ 2.0                                                                            Zn.sup.2+ 2.0                                                                       Sn.sup.4+ 2.0                                                                       2.0                                                                               6260                                                                              63                                                                               342                             Comp. Ex 5                                                                            0.05                                                                              0.375                                                                             0.375                                                                             0.250                                                                             --        --   --   -- 3830                                                                              62                                                                               259                             __________________________________________________________________________

EXAMPLES 14 TO 16, AND COMPARATIVE EXAMPLE 6

PbO, ZrO₂, TiO₂, MgCO₃, Nb₂ O₅, SrCO₃, La₂ O₃, ZnO, SnO₂ and MnO₂ were weighed in proportions which provide each composition as indicated in Table 4, pulverized and admixed in a ball mill. The pulverized admixture was processed as in Example 1 to prepare of a ferroelectric ceramic material, which was tested for various electric properties.

The results are shown in Table 4.

                                      TABLE 4                                      __________________________________________________________________________            Composition                             Electric Properties                                 Group A Metal Ion                                                                        Group B Metal Ion                                                                           MnO.sub.2                                                                             Kp                                                                               d.sub.31                          a  x  y   z  p         q     r    N (wt %)                                                                             ε                                                                         % × 10.sup.-12                                                             m/V     Qm                 __________________________________________________________________________     Example 14                                                                            0.05                                                                              0.375                                                                             0.375                                                                              0.250                                                                             La.sup.3+ 2.0                                                                            Zn.sup.2+ 2.0                                                                        Sn.sup.4+ 2.0                                                                       2.0                                                                              0.2 4850                                                                              59                                                                               240     720                Example 15                                                                            0.05                                                                              0.375                                                                             0.375                                                                              0.250                                                                             La.sup.3+ 2.0                                                                            Zn.sup.2+ 2.0                                                                        Sn.sup.4+ 2.0                                                                       2.0                                                                              0.5 2900                                                                              55                                                                               173     1080               Example 16                                                                            0.05                                                                              0.375                                                                             0.375                                                                              0.250                                                                             La.sup.3+ 2.0                                                                            Zn.sup.2+ 2.0                                                                        Sn.sup.4+ 2.0                                                                       2.0                                                                              1.0 1970                                                                              52                                                                               138     1180               Comp. Ex 6                                                                            0.05                                                                              0.375                                                                             0.375                                                                              0.250                                                                             --        --    --   --                                                                               0.5 1740                                                                              53                                                                               129     970                __________________________________________________________________________

Table 4 reveals that in the ferroelectric ceramic material [I] having a composition of the formula:

    Pb.sub.0.95 Sr.sub.0.05 (Mg.sub.1/3 Nb.sub.2/3).sub.0.375 Ti.sub.0.375 Zr.sub.0.250 O.sub.3,

having incorporated with La³⁺ in the A sites and with Zn²⁺ and Sn⁴⁺ in the B sites, as the amount of MnO₂ incorporated is increased, the mechanical quality factor Q_(m) of the material is increased while the piezoelectric strain constant d₃₁ of the material is decreased. It has been confirmed, however, that when compared with the ferroelectric ceramic material [I] having incorporated with MnO₂, according to Comparative Example 6, the ferroelectric ceramic materials according to the invention whose mechanical quality factor Q_(m) have been increased to a comparable level of that of the material of Comparative Example 6 by addition of MnO₂, still have a larger piezoelectric strain constant d₃₁.

EXAMPLE 17

Example 15 was repeated except that the La₂ O₃ was replaced with the equimolar amount of Nd₂ O₃ to prepare a ferroelectric ceramic material, which was tested for electric properties.

The results are shown in Table 5.

EXAMPLES 18 TO 20, AND COMPARATIVE EXAMPLES 7 TO 9

The ferroelectric ceramic materials of the formula:

    Pb.sub.1-a Sr.sub.a (Mg.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y Zr.sub.z O.sub.3 [x+y+Z=1],

wherein the coefficients a, x, y and z are different from those of the ferroelectric ceramic material used in Examples 14 to 17, as indicated in Table 5, with (Examples 18 to 20) or without (Comparative Examples 7 to 9) La³⁺, Zn²⁺ and Sn⁴⁺ in amounts indicated in Table 5 incorporated therein and containing 0.5% by weight of MnO₂, were prepared and tested for electric properties in the manner as described in Example 1.

The results are shown in Table 5.

EXAMPLE 21 AND COMPARATIVE EXAMPLE 10

Ferroelectric ceramic materials were prepared and tested in the same manner as described in Example 15 and Comparative Example 6, except that the SrCO₃ was replaced with the equimolar amount of BaCO₃.

The results are shown in Table 5.

                                      TABLE 5                                      __________________________________________________________________________            Composition                             Electric Properties                                 Group A Metal Ion                                                                        Group B Metal Ion                                                                           MnO.sub.2                                                                             Kp                                                                               d.sub.31                          a  x  y   z  p         q    r    N  (wt %)                                                                             ε                                                                         % × 10.sup.-12                                                             m/V     Qm                 __________________________________________________________________________     Example 17                                                                            0.05                                                                              0.375                                                                             0.375                                                                              0.250                                                                             Nd.sup.3+ 2.0                                                                            Zn.sup.2+ 2.0                                                                       Sn.sup.4+ 2.0                                                                       2.0                                                                               0.5 2770                                                                              53                                                                               165     1200               Example 18                                                                            0.05                                                                              0.500                                                                             0.370                                                                              0.130                                                                             La.sup.3+ 2.0                                                                            Zn.sup.2+ 2.0                                                                       Sn.sup.4+ 2.0                                                                       2.0                                                                               0.5 2840                                                                              52                                                                               167     1140               Comp. Ex 7                                                                            0.05                                                                              0.500                                                                             0.370                                                                              0.130                                                                             --        --   --   -- 0.5 1870                                                                              48                                                                               121     1180               Example 19                                                                            0.05                                                                              0.130                                                                             0.430                                                                              0.440                                                                             La.sup.3+ 2.0                                                                            Zn.sup.2+ 2.0                                                                       Sn.sup.4+ 2.0                                                                       2.0                                                                               0.5 2230                                                                              52                                                                               143     1110               Comp. Ex 8                                                                            0.05                                                                              0.130                                                                             0.430                                                                              0.440                                                                             --        --   --   -- 0.5 1540                                                                              48                                                                               109     930                Example 20                                                                            0.03                                                                              0.375                                                                             0.375                                                                              0.250                                                                             La.sup.3+ 3.0                                                                            Zn.sup.2+ 1.5                                                                       Sn.sup.4+ 3.0                                                                       1.67                                                                              0.5 1780                                                                              54                                                                               138     1090               Comp. Ex 9                                                                            0.03                                                                              0.375                                                                             0.375                                                                              0.250                                                                             --        --   --   -- 0.5 1370                                                                              50                                                                               110     930                Example 21                                                                            0.05                                                                              0.375                                                                             0.375                                                                              0.250                                                                             La.sup.3+ 2.0                                                                            Zn.sup.2+ 2.0                                                                       Sn.sup.4+ 2.0                                                                       2.0                                                                               0.5 2740                                                                              55                                                                               170     990                Comp. Ex 10                                                                           0.05                                                                              0.375                                                                             0.375                                                                              0.250                                                                             --        --   --   -- 0.5 1660                                                                              48                                                                               119     1010               __________________________________________________________________________ 

What is claimed is:
 1. A ferroelectric ceramic material which is a Perovskite solid solution, which comprises a solid solution represented by the formula:

    Pb.sub.1-a M.sub.a (Mg.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y Zr.sub.z O.sub.3

wherein M is Ba or Sr, x+y+z is 1, a is from 0 to 0.10, x is from 0.05 to 0.70, y is from 0.25 to 0.50 and z is from 0.05 to 0.70, containing in said solution at least one oxide selected from group A noted below and at least one oxide selected from group B noted below: Group A: La₂ O₃ and Nd₂ O₃ ; Group B: ZnO, SnO₂ and Ta₂ O₅ wherein the metal ions of the oxide selected from group B are present in the Perovskite solid solution in such an amount so that the relation:

    0.5≦N≦5.0

is met, in which N is defined by the equation: ##EQU5## wherein n_(Ai) and n_(Bj) are valencies of metal ions of the oxides of groups A and B which are present in the solid solution, respectively, and x_(Ai) and x_(Bj) are atom equivalents of metal ions of the oxides of groups A and B which are present in the solid solution, respectively.
 2. The ferroelectric ceramic material of claim 1, wherein a metal of at least one oxide selected from the group A is present in the Perovskite solid solution in the form of La³⁺ or Nd³⁺.
 3. The ferroelectric ceramic material of claim 2 wherein the metal ions of the oxide selected from the group A are present in the Perovskite solid solution in an amount of from 0.5 to 5.0 atom equivalents based on 100 atom equivalents of the sum of Pb and M present in the Perovskite solid solution.
 4. The ferroelectric ceramic material of claim 1, wherein a metal of the oxide selected from the group B is present in the Perovskite solid solution in the form of Zn²⁺, Sn⁴⁺ or Ta⁵⁺.
 5. A ferroelectric ceramic material which is a Perovskite solid solution, which comprises a solid solution represented by the formula:

    Pb.sub.1-a M.sub.a (Mg.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y Zr.sub.z O.sub.3

wherein M is Ba or Sr, x+y+z is 1, a is from 0 to 0.10, x is from 0.05 to 0.70, y is from 0.25 to 0.50 and z is from 0.05 to 0.70, containing in said solution at least one oxide selected from group A noted below and at least one oxide selected from group B noted below, said solution further containing in said solid solution M_(n) O₂ : Group A: La₂ O₃ and Nd₂ O₃ ; Group B: ZnO and SnO₂ wherein the metal ion of the oxide selected from group B is present in the Perovskite solid solution in such an amount so that the relation:

    0.5≦N≦5.0

is met, in which N is defined by the equation: ##EQU6## wherein n_(Ai) and n_(Bj) are valencies of metal ions of the oxides of groups A and B which are present in the solid solution, respectively, and x_(Ai) and x_(Bj) are atom equivalents of metal ions of the oxides of groups A and B which are present in the solid solution, respectively.
 6. The ferroelectric ceramic material of claim 5, wherein a metal of the oxide selected from the group A is present in the Perovskite solid solution in the form of La³⁺ or Nd³⁺.
 7. The ferroelectric ceramic material of claim 6, wherein the metal ion of the oxide selected from the group A is present in the Perovskite solid solution in an amount of from 0.5 to 5.0 atom equivalents based on 100 atom equivalents of the sum of Pb and M present in the Perovskite solid solution.
 8. The ferroelectric ceramic material of claim 5, wherein a metal of the oxide selected from the group B is present in the Perovskite solid solution in the form of Zn²⁺ or Sn⁴⁺.
 9. The ferroelectric ceramic material in accordance with claim 6 wherein the MnO₂ is present in the solid solution in an amount of from 0.1 to 2.0% by weight.
 10. The ferroelectric ceramic material of claim 1, wherein metal ions of oxides of group A and metal ions of oxides of group B are incorporated into A sites and B sites of an ABO₃ type Perovskite crystal, respectively.
 11. The ferroelectric ceramic material of claim 5, wherein metal ions of oxides of group A and metal ions of oxides of group B are incorporated into A sites and B sites of an ABO₃ type Perovskite crystal, respectively.
 12. The ferroelectric ceramic material of claim 5, whereina is from 0.01 to 0.07, x is from 0.10 to 0.60, y is from 0.30 to 0.45, and z is from 0.10 to 0.60.
 13. The ferroelectric ceramic material of claim 5, whereina is from 0.01 to 0.07, x is from 0.10 to 0.60, y is from 0.30 to 0.45, and z is from 0.10 to 0.60. 